Actor Tracy Morgan of '30 Rock' arrives for the 2010 White House Correspondents Dinner May 1, 2010 at a hotel in Washington, DC.

This story was most recently updated on June 8 at 4:51 p.m. ET

A truck driver involved in the six-car crash that left one dead and comedian Tracy Morgan in critical condition turned himself in to police, according to multiple reports.

Kevin Roper, a 35-year-old truck driver from Georgia, was behind the wheel of a tractor trailer that struck Morgan's limo bus early Saturday on the New Jersey Turnpike. Roper is charged with one count of death by auto and four counts of assault, and turned himself in to New Jersey State Police Saturday night, according to the Associated Press. Roper was later released on $50,000 bail Saturday.

Morgan's driver told ABC News on Sunday that he "heard Tracy screaming for help" after the crash, but couldn't reach him or others.

"We didn't know which way was up, which way was down. I don't know if we flipped several times or one time," Tyrone Gale, the driver, said. "I saw the condition of everybody, and I knew it would just make it worse if I tried to pull them up and out of the vehicle."

James McNair, a comedian and friend of Morgan's, died in the crash. Morgan remained in critical condition overnight.

“His family is now with him and he is receiving excellent care,” Lewis Kay, Morgan's publicist, told The New York Daily News on Saturday. “We don’t anticipate much of a change in his condition today.”

Walmart confirmed on Saturday that Roper was driving one its trucks, and promised to take "full responsibility" if the truck was determined to be cause of the accident.

“Safety is our absolute highest priority, but that is no comfort whatsoever to the families and friends who are suffering today," the company said in a statement. "We offer them our deepest condolences. We can’t change what happened, but we will do what’s right for the family of the victim and the survivors in the days and weeks ahead.”

UPDATE: A spokesperson for Tracy Morgan says the comedian is "more responsive," but will likely remain in the hospital for "several weeks."

"While Tracy remains in critical condition, he has been more responsive today, which is an incredibly encouraging sign," the rep said in a statement. "He sustained a number of injuries, including a broken leg, a broken femur, a broken nose and several broken ribs. He had surgery earlier today on his leg. We expect him to remain in the hospital for several weeks. His family is tremendously overwhelmed and appreciative of the outpouring of love and support from his fans."